Conformation of substituted polyacetylenes in solution :
relationship between electronic properties and local
order
P. Garrin, J. Aimé, J. Fave, S. Ramakrishnan, G. Baker
To cite this version:
P. Garrin, J. Aimé, J. Fave, S. Ramakrishnan, G. Baker. Conformation of substituted polyacetylenes in solution : relationship between electronic properties and local order. Journal de
Physique II, EDP Sciences, 1992, 2 (3), pp.529-546. <10.1051/jp2:1992147>. <jpa-00247648>
HAL Id: jpa-00247648
https://hal.archives-ouvertes.fr/jpa-00247648
Submitted on 1 Jan 1992
HAL is a multi-disciplinary open access
archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d’enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.
J.
Fhys.
II
France
(1992)
2
529-546
1992,
MARCH
529
PAGE
Classificafion
Physics
Abstracts
36.20
46.90
71.90
Conformation
of
substituted
electronic
between
relationship
(I),
Garrin
P.
G. L.
J. P.
Aims
*), J.
(1>
polyacetylenes
properties
(I),
Fave
L.
solution
in
and
(2) and
Ramakrishnan
S.
:
order
local
(3)
Baker
(1) Groupe de Physique des Solides,
05, France
Cedex
(2) Dept of Inorganic and Physical
Universit£
VII,
Paris
Chemistry,
Indian
23, 2 place
Tour
of
Institute
Jussieu,
75251
Paris
Bangalore-560012,
Science,
India
(3)
Bellcore,
(Received
331
Springs Road,
Newman
September1991,
ii
revised
Red
28
New-Jersey
Bank,
accepted
1991,
October
07701-7040,
15
U-S-A-
1991)
November
Nous pr£sentons
Etude de la
conformation
solution
du polyph£nylac£tylbne
et
une
en
poly(2-octyne). Ces deux polymbres ont des
diff£rents
trbs
la
solution
de
comportements
polyph£nylac£tyl~ne est rouge alors que celle de poly(2-octyne) est transparente et (es longueurs
statistiques mesur£es
respecfivement 45 et 135 h. L'£tude de ces deux systdmes nous permet
sont
de
d£duire
fluctuation
courbure
Electrons
la
de
joue un rble mineur sur la localisation
des
que
Elle
£galement de
du squelette.
unit£s
monomdres
montrer
permet
entre
nous
que la torsion
ar
conformation
responsable de la localisation
des
Electrons
d'expliquer la
statistique des
est
et
ar
R4sumk,
du
ch@mes.
red
has
solution
observed
:
systems,
and
study of the chain
performed. The two
while
poly(2-octyne) is
the
statistical
length are
A
Abstract.
octyne)
been
one
the
that
conformation
1.
deduces
that
torsion
between
and
the
in
polymers
and,
transparent
45
h
and
units
monomer
solutions
differ
play
is
in
the
polyphenylacetylene
of
many
marked
a
h
135
fluctuations
curvature
electrons
ar
conformation
respectively.
a
minor
role
pertinent
poly(2-
and
polyphenylacetylene gives a
ways
difference
the chain rigidity is
on
From
on
the
parameter
the
study of these two
localization,
electrons
ar
understand
to
the
chain
localization.
Introduction.
Conjugated polymers with large molecular
substituents.
solvents by adding appropriate
weights
Most
can
exhibit
be
Solubilized
therrnochromism
in
common
and
organic
solvatochrom-
optical properties and
relation
between
studies
the
on
provide the
homogeneous
solutions
of
macromolecules
can
opportunity to study the single chain properties.
The
of conjugation
notion
length is widely used to explain the visible absorption and the
Resonant
Raman
Scattedng (R.R.S.) results [1, 2]. It is a useful
phenomenological
parameter
ism,
which
(*)
351,
Present
cours
de
address
la
extensive
stimulated
has
conformation.
chain
Moreover
Laboratoire
Lib£ration,
33405
de
Cristallographie et Physique
Cedex,
France.
Talence
Cdstalline.
Universit6
Bordeaux
1,
530
JOURNAL
describing
along
PHYSIQUE
DE
N° 3
II
backbone,
and is
related
overlap
to the
average
be
decreased
by
torsional
overlap
curvature
or
can
ar
fluctuations, the location of the maximum
optical absorption in the visible spectrum as well as
is explained as a direct
its
broad
and
structureless
character
of the
statistical
consequence
conformation
of the polymer [3]. On the other hand, the role of conjugation
considered
was
for
understanding
of
primary
importance
stiffness
the
local
scale,
suggesting
that
at
conjugated polymers should
exhibit
[4,
5].
This
saturated
greater rigidity than
concept
ones
obtained
in part supported by the
results
from the
polydiacetylenes
P4BCMU,
P3BCMU
was
orbitals.
electrons
Since
the
the
[6, 7].
PTSI2
and
delocalization
electron
between
Conversely,
monomer
increasing
studies
recent
units
play
key
a
of
amount
in
theoretical
emphasizing
fluctuations,
shown
have
role
their
that
substituents
the
understanding the
has paid special
work
influence
the
on
torsion
the
attention
effects
the
to
between
[8, 9]
conformation
electrons
gr
and
statistical
of
and
an
torsional
[10-13].
delocalization
experiments aiming to establish
accurately as possible the
paper
we
as
description of the chain statistics, to predict its link with the gr electrons
delocalization.
Small
Scattering (SANS) was used to provide
Angle Neutron
structural
information
intermediate
at
200 and 10 I. Then the chain
and local
scales, that is between
conformation
related
to
was
In
visible
with
out
describe
this
R-R-Sabsorption
and
spectroscopy
polydiacetylene and polythiophene
Here
(RC
=
focus
we
CR')~.
PPA),
abbreviated
work
our
this
In
where
give
we
R
H
two
R'
and
octyne),
2.
2,I
which
structure
where
CH~
R
=
Experimental
SAMPLE
confirmed
not
was
and
already
have
been
carried
polyacetylenes
generic
formula
is
whose
(hereafter
polyphenylacetylene
examples. One is
C~H~, for which NMR experiments suggested a
by R.R.S. [15-17]. The second
the poly(2concems
=
=
helical
studies
[7, 14].
derivatives
substituted
on
note,
Several
results.
R'
=
CH~)4CH~,
as
a
model
system.
section.
Using
DESCRIPTION.
pentachlodde (Mocl~)
larger than 10~. With
Masuda
these
catalysts,
two
(WCL)
hexachloride
tungsten
catalysts,
polymerized
polymerization of
[15]
al.
et
PPA
molybdenum
weight
and
to
a
molecular
polyacetylenes
soluble
with
properties :
govem
was
cocatalyst and even the solvent used for the polymerization. Here the synthesis
the catalyst,
with WCL and the cocatalyst Snme~,
instead
of WCL/Sn~P4 used by
done in
toluene
has been
PPA
solution
absorbs
(paragraph 2.3,I) than the
Abe et al. [16]. The
longer wavelength
at
polydispersity
weight of 49000
with
obtained
by Abe et al. [16]. A
molecular
a
one
measured
by G-P-C(MJM~) of 1.35 have been
675 000 with a polydispersipoly(2-octyne) sample, the molecular weight is M~
For the
520 ± 20 h. In spite of the
ty 1.8. The light scattering study yielded a radius of gyration Ro
showing the same optical properties as
conjugated backbone, the solution
transparent,
was
saturated
polymers.
common
various
[15].
achieved
substituents
Numerous
the
parameters
polymer
=
=
2.2
SANS
Dl1,
q is
D17
the
Neutron
METHODOLOGY.
Laue-Langevin
on
wavelengths used
and
scattering
5
were
D16,
vector
m
and
8
scattering
Dl1,
diffractometers
the
I,
3.46
corresponding
defined
by
to
D17
m
and
the
0
the
scattering
angle
and
A
12
D16.
I
range
6
were
and
I
x
10~
performed
sample-detector
The
m
~
i~
~
q
Institut
distances
and
A, respectively
4.56
and
the
at
~
0.25
i~
~,
for
where
:
q=~"sin
with
experiments
and
the
neutron
~
incident
(l)
wavelength.
CONFORMATION
N° 3
studied
macromolecules
The
the
collected
data
from
on
background with
intensity given by
solvent
scattering
providing
scattering
the
monomer
chains
between
gyration
of
the
on
macromolecule
an
function
normalized
to
P(q) is
Avogadro's
where
is
such
defined
number
and
(q)
m
=
is
K
often
more
the
chain
for
radius
a
thorn
point
convenient
has
to
are
checked
scattering
the
use
was
which
been
:
M~
P
is
m
the
(2)
(q )
molar
factor
contrast
defined
of
mass
by
the
unit,
monomer
:
v~
£af--£a)
K=
a
of
radius
the
measured,
are
the
and
interference
smaller
This
The
gives
interaction
I.e.
the
of
within
fluctuations
scale
regime.
=
=1,
the
statistics.
function
range,
interchain
colTelations
S(q
the
l,
length
diluted
~
P(0)
that
of
to
Guinier
a
obtained,
chain
interchain
due
the
~
to
thus
was
the
average
on
corrected
was
normalized
autocorrelation
the
intrachain
in the
weight
molecular
the
g
A'
l)
~
concentration
experiments.
q range in the present
isolated
is
measured,
it is
chain
state
whole
the
Ro(qRo
of
it
and
density-density
of the
latter being
; the
scattering function. In
Ro, in the range qR~
extrapolation
method.
At
by using the Zimm
of gyration of the polymer
normally independent of the
When
Contributions
Then
measurement
of
the
removed
in
transform
isotropic
an
I-L-L-
at
determination
considered
also
were
dependence
concentration
available
Absolute
accurate
Fourier
thus
performed.
was
routines
[18].
cell
allowed
intensity S(q) is the
density (p (r) p (0)).
solution,
in
detector
current
water
a
which
constraint
a
isotropically
scatter
two-dimensional
the
531
POLYACETYLENE
SOLUBLE
OF
(3)
u
s
,
where
at
and
v~
is the
assumed
to
be
the
of
volumes
molar
Scattering Jknction ofchain
2.2. I
thread,
thin
a
are
the
solvent
and
units
monomer
scattering length of the atom I. Note that in equation 3
point
with a scattering length density
obtained
scatterer
the
from
the
chain
as
and
unit
monomer
average
is
of
contributions.
atomic
all
v~
coherent
,
focus
we
attention
conformation
asymptotic regime
simplicity we consider two
Considering
length.
statistical
with
on
at
local
the
scale.
a
In
other
infinitely
an
words,
we
are
scattering
function,
that
is, g(q) oz q~" for
For
asymptotic laws : a q~ ~ law for the Gaussian coil (with
oJ.
q
excluded
volume
effect and for very large chains, the exponent is given by «
1/0.6 [19])
an
q~~
and
law
for
of
dimensionless
function
the
rod.
The
the
scattering
a
purpose
regime. For
g(q) is to obtain the scattering density of the
macromolecule
in the asymptotic
of the rod
conformation,
the
defining M~ as the mass per unit length, the limit of
case
g(q) is given by :
interested
in
-
the
the
of
>
~M~
qg(q)=j
rim
where
linear
is
u
angular
is
the
density
correlation
observed.
The
half
the
of
unit
monomer
of the
length.
macromolecule
along
rigidity
statistical
is
Therefore
in
a
the
~
plateau height
conformation.
rod
(4)
~i
For
an
in
a
actual
qg(q)
plot gives
the
chain,
the
wormlike
large enough such that a rigid
conformation
is
measured
by the statistical length b (or the persistence length, which
length) and defined by equation (5) [20] :
the
backbone
can
be
JOURNAL
532
2[ Ii
(ti t2)
where
the
t;
vectors
(. Therefore,
one
scattering regimes
Actually,
Yoshisaki
with
finite
if
worm-like
a
in
and
do
not
a
q~
shows
that is
scale
model)
by equation (6) [21]
~
q~
a
behavior,
~
backbone
have
behavior
chain.
For
at
a
q~
is
u
the
rod
the
=
+
=
N
is
Nu
such
the
behavior
a
contour
=
be
will
length)
the
(6)
4/3
for
larger
is
for
2
[7].
units
monomer
infinite
an
observed
thorn
of
qb
7
m
long
as
thickness.
conjugated polymers
Effect of chain
Because
differ
from
polymers
they
markedly
common
polystyrene. In most practical cases, it is not enough to have
infinitely thin thread. As we show
scattering
function
for an
factor
dimensions
of the
chain
modify the
structure
at large
need
such
chain
with
finite
go(q)
is
describes
often
are
24]. A well
radius
now
the
the
effect
of
for
the
the
of
finite
the
lateral
the
by
be
can
is to
the
use
corresponding to the infinitely thin thread and
side-groups.
Approximate
expressions
for
whole
the
scattering
investigated
[23,
vector
range
approximation. Setting R), the mean
Guinier
square
dimension,
lateral
(7)
substituent
describing
for
approach
gyration
of
factor
structure
sufficient
known
variation
the
be
and
general form of
approximated
The
q.
to
go(q) 4~(q)
=
where
substituents
polyisoprene
as
:
g(q)
~P(q)
~P(q)
large
part 3,
in
dimensions
lateral
ratio
general
the
chain, with
[22]. More
L/b (where
the
chain
the
as
solubilized,
for
in
worm-like
2.2.2
scattering
function
equation (7) [23, 24]
with a persistence
asymptotic behavior
Ub
number
the
C (oJ)
and
=
quantitatively
L
for
chains
[2 Ii. They proved that
w
-
length,
unit
monomer
2N~~
measured.
~~
~
I
(q)
g
U
q
where
is
wormlike
that
chain
a
different
:
lim
C (N )
to
chain,
worm-like
abscisse
observe
function
values
low q
curvilinear
can
demonstrated
correspond
should
it
the
at
polymer, we
the
scattering
which
at
(Y.Y,
exhibit
the
to
fairly rigid
a
worm-like
helical
a
the
on
Yamakawa
lengths
chain
for
(5)
~
tangent
that
N° 3
II
l~[
eXP
"
vectors
expect
depending
contour
curvature,
described
is
unit
are
can
PHYSIQUE
DE
for q
~
~P
R~
(q)
is
written
q~R)
(q)
lP
To
describe
section
is
ribbon,
2.3
or
stable.
To
with
chain
a
function
address
at
this
helical
Optical and R-R-SDegradation effects
months.
In
colorless
room
scattering
a
exp
larger
simple
values,
q
a
This
will
precise
more
geometrical
sections.
cross
(8)
~
form
be
be
can
discussed
description
used
in
e-g-
of the
detail
more
cross
cylinder,
a
in
a
3.1.3.
RESULTS.
2.3. I
were
the
needed.
=
results.
It
observed
are
has
been
in
films
reported
kept
[15]
at
that
room
films
of
PPA
for
temperature
solution, the PPA samples degrade in a much
shorter
time : the
In
order
degradation,
day
at
temperature.
prevent
to
a
room
temperature.
at
5 °C.
For
the
stable
poly(2-octyne),
all
experiments
the
were
not
about
solutions
within
performed
are
very
three
become
experiments
performed
at
CONFORMATION
N° 3
The
red
the
:
poly(2-octyne)
absorption
absorption
spectrum
absorbs
in
maximum
is
suggests
delocalization
electron
located
range
at 450
larger
than
3500
4000
(below
nm
nm).
280
with
a
tail
For
for
the
solution
(Fig. I).
corresponding
650nm
to
up
PPA,
conjugation lengths
poly(2-octyne).
distribution
broad
a
much
U-V-
the
533
POLYACETYLENE
SOLUBLE
OF
of
is
The
to
an
o.D.
2.00
1-so
i.oo
o.50
0.00
3000
Fig.
I.
used
for
Visible
R-R-S-
is
For
often
I,
of
analyze
the
5500
PPA
in
Arrows
toluene.
6@~0
6500
indicate
excitation
the
wavelength
too
to
backbone
structure
side-groups
substituent
with
much
a
of
distribution
and
complicated
more
conjugation
analysis is
in the film and
useful for comparing
local
structure
4 579 I and
between
wavelengths of our lasers
were
PPA,
Ramart
poly(2-octyne) absorption to be still
For
far from the
resonant.
solution
different
wavelengths both for the film and the
obtained
been
at
intensities
of the two peaks
studies
excitation
wavelength, an inversion of the
of
but
The
have
spectra
(Fig. 2). In
used
samples
[17],
solution.
6 400
spectrum
5000
R-R-S-
lengths.
required
the
Absorption
4500
wavelengthlA)
technique
the
was
still
excitation
available
I(a.u.)
1(a.u.)
1.5
2.5
2.0
1-o
1.5
~~~
i.o
6yyiA
(i)
o.5
(II)
58o5A
o_~
0.0
0.0
400
700
1000
E(cm
1300
1350
1600
1450
1550
E(cm
~)
b)
a)
Fig.
2.
a)
Raman
spectrum
correspond to the
incident
wavelength in
solution
the
JOURNAL
DE
PHYSIQUE II
-T
2,
1650
~)
of
PPA
solvent
N'3,
in
toluene.
solution
b)
(I)
Evolution
film
and
of
the
(II).
double
Additional
bonds
lines
sharp vibrational
frequency as a function
solution.
MARCH
lW2
2'
in
of
534
JOURNAL
500
around
film
changes
drastic
reminescent
of
[17],
except
films
spectral
taking
the
chain
those
of
the
light
curvature
Batchelder
rotation
or
al.
et
difference
spectra
units.
monomer
sample
solutions
and
nearly
are
identical
isomerisation
induce
similar
a
films
the
the
between
for
obtained
between
3
N°
:
Our
they
that
or
spectra
found
are
PPA
called
have
we
in
process
that
II
the
frequencies suggesting a higher degree of order.
Without
main
chain
the
phenyl
and
vibrations,
they proposed a
account
however, they recognized that this analysis was not entirely conclusive,
structure
results
being seemingly in
contradiction
with the IR and
NMR
data.
maxima
lower
at
are
coupling
into
trans-cisoid
Ramart
the
in
for
II
(C=C stretching) was
observed.
Also,
solubilization
suggesting that
does
not
cur
solution,
and
PHYSIQUE
DE
between
2.3.2
SANS
results.
After
hour of collecting data,
observed
of the
decrease
one
we
a
scattering intensity at low q values at room
for PPA (Fig. 3). This
observation
temperature
directly related to a drastic loss of molecular weight. The degradation process not only
was
conjugation length as
shortens
the
shown
by the
disappearance of the visible
optical
absorption, but also breaks the chain itself. Thus, in order to prevent sample degradation, the
experiments
performed at 5 °C. At this
degradation is
controlled
and
temperature,
were
we
noticed
only a slight decrease of the scattering intensity at low q after one day (Fig. 3). We
discuss
thus
the
performed at 5 °C keeping in mind that we do not have the
measurements
sample quality as for poly(2-octyne).
same
g(q'~)
300.00
~g<q~>
?~
250.oo
,
+
3m
~
$~
o~O
°*~b
200.00
~oo
w
iso.oo
,oo
~
w
o
loo_oo
w~
coo
ooi
ooj
o~
o-m
oos
oo~
~
50.oo
0.00
0.00
0.04
0.02
Fig. 3.
chains
Decrease
temperature
The
shown
do
not
5 °C
4.
can
accurate
scattering
negligible.
functions
at
due
vectors
to
of
the
different
the
concentration
for
the
(q>0.45i~~)
the
value
done.
The
1.2
of
in the
the
q
and
0.6
of
the
m
x
6
PPA
the
room
contribution
~
of
the
order
measurements
of
the
carbon
are
we
The
g cm~ ~.
belonging
atoms
[25]. In
table
protons,
samples
~ i~
~,
10~
x
10~
cross-section
incoherent
given
section
cross
were
the
vectors,
contribution
incoherent
from
comes
from
between
poly(2-octyne)
and
value
incoherent
equation (9),
polyphenylacetylene
of the scattering
for
lowest
contribution
significantly
Using
the
corrected
are
main
estimation
of the
to
=
effect
any
functions
be
scattering intensity as a function of time, due to the degradation
(b) (O) t
0, (+) after 10 hours. The inset figure corresponds
(O) t
0, (+) after 6 hours, (D) after 12 hours.
scattering
Except
observe
The
o-lo
l~~~)
vectors
=
measurements
figure
chain.
which
at
measured
in
scattering
the
of the
solution
in
0.08
0.06
scattering
to
protons,
to
have
at
an
large
atoms
is
N° 3
CONFORMATION
535
POLYACETYLENE
SOLUBLE
OF
g~q~)
500.00
~
400.00
~~
~~ ~~
~V
ix
200.00
'~~
o
100.00
~°O~~~~~~~
°Cooc~~*4wmx,~
~~°°°°°°°~°
0.00
0.00
0.01
0.02
0.03
q
Fig.
0.05
1.2
c
Helix
I.
Table
parameters
given
are
unit
Monomer
for the refinement of
Angstrom.
used
parameters
in
L~
P
0.6 mg/cm~
poly(2-octyne ) scattering function.
the
L
b
aR
b
structure
trans-transoid
cis-trartsoid
where
n~
is
«(~m
100
bams
table
the
«(~
:
number
with
the
20
6
1.78
135
10
15
6.5
1.33
135
l10
15
6
1.72
135
102
of
protons
wavelength
shown
=
for
qg(q)
a
unit
monomer
transoid
or
plot,
length
with
u
4.56
significantly
30, thus
=
subtraction
contribution
~
R'
R
R
Different
trans-cisoid
q.
(c).
possible
a
of
the
in
the
found
value
/
of
structures
~
~
for
the
~'
for
conformation
1.29,
to
must
be
and
while
close
/
~/~
to
while
at
trans-transoid
using
for
a
cis-
a
1.20.
The
R
i~_~/
/
~
backbone
q
poly(2-
2 fb,
about
low
at
the
20 fb.
about
~
R
polyacetylene
example,
of
contribution
effect
R'
~i-
R'
negligible
~
R'
'_(~
R
incoherent
the
For
polyacetylene in a
trans-transoid
the plateau height
be
close
must
conformation
(Fig. 5) with u
2.61 A, it
<a>
5.
the
contribution
incoherent
an
incoherent
an
large
at
has
A,
,~/~,~/~,~/
(b),
estimation
an
than
by subtracting
obtained
This
R
Fig.
larger
(much
=
R'
R
gives
unit,
monomer
I
a
2.43
=
trans-cisoid
a
the
are
PPA.
curve
=
=
For
in
A'=
bams).
81
scattering functions
0.6 for poly(2-octyne)
and 0.3
values, but it may change the
0.05 A~
octyne) at q
g(q, c)
h~
0.2
g(q, c)
3.I, thus
q
final
The
~
=
=
=
=
The
0.06
~i~')
concentrations.
PPA : c
Scattering function of PPA and poly(2-octyne) at two
mg/cnl~
~ (D),
0.6
mg/cm~~ (+)
1.2
(O).
poly(2-octyne)
mg/cm~
c
c
4.
(x),
0.04
'~~
~
~
~.
(a),
cis-transoid
536
JOURNAL
difference
between
the
experimental
is
values
two
PHYSIQUE
DE
7.5fb
about
II
N° 3
approximately
is
which
within
the
by equation (6), such a plateau will also be observed
with a
error.
worm-like
chain
when
the
statistical
length is sufficiently large.
In figures 6 and 7, the qg(q, c) and q~g(q, c) plots are
shown.
of poly(2For the
case
octyne), the qg (q, c) plot does not show the expected value for the plateau height. The value
is 1.48 : I-e-, it is 15 fb higher than the
calculated
for the
measured
value
trans-transoid
conformation
discrepancy
is
difference
a
23fb
much
solvent
larger than the experimental
height measured in various
about
5 fb
of
paragraph 3.
At large
values
PPA
between
higher
and
deuterated
the
shown
As
and
from
the
than
for
one
calculated
the
trans-cisoid
in
accuracy
values.
(toluene,
sizeable
of the
scattering
obtains
vector,
one
poly(2-octyne) (Fig. 7). PPA shows a
variation
THF,
difference
completely
a
of
the
This
example
DMF...) gives
For
measurements.
our
experiments
This
the
conformation.
is
discussed
in
different
behavior
scattering
function
qg<q~)~h-~)
5
o
4
3
2
1
0
0.00
0.05
0.15
0.10
0.25
0.20
q~i~')
Fig. 6.
by the
[2 Ii).
For
PPA
the
27, b
=
45.3
M~
correspond
g
=
h, R~
to
mole~' h~
effect
3
h.
For
poly(2-octyne) (O)
~P
(q),
used
is
is
M~
39. I g
=
poly(2-octyne),
deuterated
chain
A~
mole~
helical
An
~.
serie
structure
given
in
the
at
fit
the
local
is
colTesponds
assumed
corresponding
scale
is
to
for ~P
used
a
are
the best fits
for
go(q) (Ref.
Lines
toluene.
model
~P(q)=exp(-q~R)2).
by
modelled
in
wormlike
the
=
second
the
gj(q)
length
unit
cross-section
46
=
per
mass
(6) and
factor
structure
The
structure.
L/b
c) plots of PPA
qg (q,
theoretical
to
The
trans-cisoid
a
parameters
trans-transoid
(q ) (see text).
structure
The
are
with
parameters
table.
qfg~q~)~i'i
/8lq,C)~'~)
0.30
0.30
0.25
o 25
~
0.20
0 20
/~'
0.15
0.15
o
~
'~
o lo
°'°~
0.05
0.00
0.00
0.00
0.05
0.15
0. lo
q
0.20
~")
0.00
0 25
0.05
are
the
same
as
0.15
0.20
0.25
~'l)
b)
scattering
figure 6.
q~ g (q, c) plots of the
7.
o-10
q
a)
fits
o
~
0.10
Fig.
o
~
A
g~6AAb6~
°
for
the
function
of
PPA
(7a)
and
poly(2-octyne) (7b). Symbols
and
CONFORMATION
N° 3
similar
3.
Discussion.
3. I
CHAIN
3,I,I
conformation.
theoretical
fit for
best
similar
PPA
and
being
the
at
A~
0.18
around
it
shows
of
the
a
q~
scattering
two
behavior
deduced
at
0.05
q
A~
m
figure
from
6
that
show
curves
~,
rigid
more
comparison
without
even
a
is
chain
PPA
the
it has
thus
to
a
factor.
PPA
for
observed
that
to
gives a statistical length
polybutylthiophene
[14].
at 5 °C
measured
polystyrene
conjugated
have
electron
delocalization
the
stiffness
of
on
increase
physical
b
45
=
The
±
5
A, suggesting
a
gyration
of
radius
is
identical
these
two
one
conformation.
chain
from
conjugation
flexibility cart
Thus,
PPA.
polymers
the
unit
monomer
of
structure
is
the
difference
might expect to
measure
On actuality,
though, PPA
not
than
more
a
only
the
structures,
from
factor
difference
between
the
is
effect
the
of
the
flexible
still
two.
with the
easily
understood
model
have
we
already used [8, 9] and that we describe
below (see paragraph 4). But, for the
of PPA,
case
understood
in another
the flexibility could also be
That is, we might argue that flexibility
way.
arises from a mixing of different
conformers.
For example, in a
trams-cisoid
structure,
transwhile not being able to
eliminate
such
transoid
defects
increase
the chain flexibility.
However,
possibility, one can note that R-R-S- results and
scattering data suggest mainly a
neutron
a
The
trans-cisoid
origin
almost
backbone
conformation
statistical
and
located
polydiacetylenes [7], that is
pronounced
decreased
a
or
A.
lo
±
polybutylthiophenes [14]
while
poly(2-octyne)
structure,
the
maximum
a
structure
flexibility
i lo
like
The qg(q, c) plots
poly(2-octyne) shows
easily be
This
can
while
The
ribbon
537
STRUCTURE.
PPA.
flexible
for
observed
those
to
corresponds to a
l~ ~, with
q m 0.2
POLYACETYLENE
SOLUBLE
OF
of
the
be
structure.
Poly(2-octyne).
A rigid
behavior
for the
poly(2-octyne) sample.
observed
was
plateau height at 1.48 in the Y.Y, model, we obtained good
accordance
between
the
a
computed
values
and the
observed
scattering
statistical
length
(Figs. 6 and 7). The
curves
fit is b
=135±
corresponding
the
lo A.
Actually,
the
theoretical
is
obtained
to
curve
differently than by simply multiplying the computed
factor by a
such
that
structure
constant
the plateau height is
reached.
follows
rationalize
why at low q the plateau
In what
will
we
height is too high and why the decrease of the scattering intensity is more pronounced thorn for
3.1.2
Setting
a
ribbon-like
structure.
information
statistics
obtained
Modelling of the
More
chain
be
cross-section.
on
can
It provides not only a more
detailed
analysis of the scattering
at larger q values.
curves
cross-section,
also
precise description of the
actual
shape of the
but
allows
better
a
extension
understanding of the whole scattering
Setting L~ as the total lateral
of the
curve.
chain
width, a
ribbon-like
and e as
the
gives a q~~ dependence in the range
structure
I/L~~q~
Since
do
observe
such
behavior,
consider
other
lie [7].
not
two
we
we
a
for describing the scattering
circular
geometrical cross
sections
at large q (Fig. 8). For a
curve
the
function
~P(q) is given by :
cross-section
3,1.3
from
a
lfi
where
(
where
the
is
the
first
Guinier
order
Bessel
approximation
(q )
function
2
=
( (qR
2
(10)
~
and R is
the
applies (Eq. (8)), R~
of the cylinder.
given by R~
RI
radius
is
=
In
/.
the
q
range
JOURNAL
538
PHYSIQUE
DE
~i1
~
II
N°
3
~~~ ~~
(a)
~b)
R
(d)
(c)
Fig.
Simple geometrical
(c), helical
structure
8.
structure
For
helical
a
describing
with
central
the
at
structure
used (~)
be
can
forms
the
scale,
local
cross-section
chain
ribbon
(a), cylinder (b),
helical
part (d).
hollow
the
by Pringle
obtained
results
[26]
Schmidt
and
:
(
(q)
~P
=
s~
H
~~~~
cos~ (ny/2)
~~~°j~ [g~(qR, a)]~
(ll)
(~°'/2)
n=0
where
g~(qR, a)
R~~(I
2
j~
a~)~
=
dr
/~~)
rJ~(qr
(12)
aR
with
and
pitch length
the
P
2grn
qn"j
with
I
s~
width
of
without
the
side
central
a
For
geometrical
s~
of
=
lengths
region,
former
case,
For
the
parameters
=
2
R
the
the
P
an
must
is
the
while
contour
effective
"~~
w
H
with
be
p
~
of
kinds
Two
second
axial
case,
and
0.
#
n
cross-section,
Fig. 8).
latter
a,
for
=
the
(see
groups
hollow
the
polymer.
and
0
n
lateral
the
structure.
of
for
=
characteristic
~
qR
I
q~
2grnR
q~
y
length
of
and
describe
helical
the
helix,
R
aR
and
arrangement
and
are
considered,
one
region defining
spring-like
length
contour
a
length is identical to the total
scattering length density dependent
~~
considered.
Let
define
us
are
the
structure
hollow
central
a
w
L~
as
=
the
on
the
total
mu
(1)
Note
that
the
I
term
given
in
reference
dropped
in
(Eq. (12)).
[26] is
already
included
in
the
q
(Eq. (7)),
thus
it has
been
For
the
length H,
see
(Eq. (15)).
function
go(q) (see
CONFORMATION
N° 3
length
contour
axis
for
helical-spring-like
is given by :
a
length
contour
OF
the
structure,
539
POLYACETYLENE
SOLUBLE
total
corresponds
length
contour
the
to
and
L~
~~~~~ ~~
~~~~
~
~
2
~/jj
Therefore,
in
Yamakawa
go(q)
the
~
total
the
given by equation (13)
is
model
(Eq. (7))
term
and
P
length
contour
in
the
instead
of
used
Also,
and
Yoshizaki
~~~
by
not
j
graR
plateau height
a
m
I,
given by
A
have
we
:
u
A=ij[1+
(~"~~)~j
P
u
thus
increase
an
Equation (I I)
which
scattering
can
be
simplified
I
for
except
=
we
=
as
n
~P
(q
as
q
w
"
cylinder,
a
compact
corresponds
This
I-e-
the
scale
For
structure.
0 remains
with n
thus only the
term
expression for the cylinder (Eq. (10)) and
in
(Eq.
serie
the
only
have
we
P
at
helical
the
which
at
qw~",
scale
the
to
P
0,
=
(ll)).
For
=
j(1
=
~
where
case
homogeneous
a
the
recover
density.
length
in the
approximated
is
structure
appears
0,
a
the
helical
the
structure
q~
of
(14)
~
j
"~~
+
~
P
qR (I
for
(( (qR )
a
~
# 0
a
have
we
:
~
aJj (aqR
(15)
)))
)
included
in the
go(q) term (Eq. (7)).
where
the
length has been dropped and
contour
Equation (15) emphasizes two main
differences
with respect to the cylinder
One is given
case.
by the prefactor, which
introduces
effective
scattering length density, and a higher plateau
an
behavior is
height in the scattering vector range where the q~
observed.
The
second
concems
the
scattering
This
effect
be
easily seen in a q~g(q) plot : the
at large q.
curve
can
more
location
of the
maximum
and the magnitude of the
decrease
govemed by a and R. For a
are
given size of the
substituent
side-group the decrease is more
pronounced for a # 0. The
different
theoretical
obtained
with
equations (7), (8), (10), (15) are shown in figure 9.
curves
Also
easily verify that equations (I I) and (15) give the same
results in the range of
can
one
where
equation (15) applies.
scattering
vectors
factor
corresponding
In
figures 6 and 7b is reported the
calculated
structure
to
b
7.8 A from
135 A, a pitch length P
15 A and for the
cross-section
0,17,
R
:
a
6.51 for the side-group. The parameters of the best
obtain
actual
length f~
which
an
we
=
=
=
=
=
fits
obtained
each
higher
percent)
All
that
these
a
different
trans-cisoid)
order
of
values
of
to
able
for
to
described
parameters,
conformation
magnitude
well
the
for
lateral
then
even
then
as
helical
a
for
one
between
the
cannot
poly(2-octyne).
dimension
eliminate
All
of
the
series
differ
only
so
small
remain
different
the
whole
the
unit
a
allows
q
any
hollow
one
the
possibility
of
of
parameters
side
for
scattering
at
(within one
In
to
substituent
identical
structures.
range.
central
with
structure
monomer
almost
are
functions
differences
the
satisfactorily
fit
factors
structure
scattering
discriminate
conformation
trans-transoid
set
and
are
calculated
computed
The
A-I,
is
The
table.
expect
cannot
we
the
structure.
0.17
than
conformation
of
use
in
parameter
statistical
with
unit
monomer
vectors
the
given
are
group
case,
the
region.
If
fit
a good
cis-transoid
(or
obtain
a
give
f~
reasonable
a
6
=
or
6.5
A.
540
JOURNAL
PHYSIQUE
DE
II
N° 3
q~g~q) ~l'~)
0.30
0.25
0.20
'~~'-",,~,fi
o.15
~'
""
o-lo
o.05
0.00
0.00
o-lo
0 05
0.15
q
Fig.
9.
length
the
concems
sponding
helical
The
for
structure
torsion
fjr
and
units
A.
1.8
of
which
4
statistical
structure
energy
of
the
per
fit
other
values
average
thus 9
poly(2-octyne)
of the
q
structure
equal
is
in
optical
both
used
R~= 3A
to
extension
L~
sides
the
lateral
total
sample
be
can
of
consistent
equal
is
to
10
markedly
differs
for
PPA.
The
with
from
the
square
ribbon-model
mean
a
A, corresponding
to
phenyl
backbone.
properties.
polyacetylenes differ in many ways : PPA has an optical transition at a
poly(2-octyne) ; the statistical
conformations
different
(the
are
very
poly(2-octyne) is about three times larger than the one of PPA), and the
cross-sections
leads
completely different
geometrical
of the
to
group
than
length
of
the
while
gives two
period and an
20A,
gives P
conformer
units
monomer
38°.
ribbon-like
a
altematively
substituted
lower
7
=
extension
the
and
trans-transoid
The
to
51°,
about
torsion
large
at
that
in
lateral
rigidity
two
much
#
h-
molt
=
function
the
and
corresponding
average
an
PPA
for
distributed
Chain
The
:
A
15
P
A
1.3
between
monomer
in
rings
parameter
45.3
=
12
=
input
The
ML
~~
R)
4.
lies
scattering
observed
radius
(q).
~P
three
=
=
units
The
one
go(q)
=
the
=
between
monomer
for
the
=
pitch length
the
is
g(q)
factors
structure
density
radius
inner
0 30
=
R
to
0.25
corresponding to the
The only change
~.
g
same
curves
4.6 h (correGuinier
approximation with R~
~P(q) full line
model
cross-section
of
dotted
line
6.5 Ji (Eq. (10)),
line : circular
cross-section
R
6.5 A) (Eq. (8)),
dashed
(15)).
7.8 A, F
15 A (Eqs. (ll)
with a
0.17, R
or
Theoretical
scattering
0 20
~i'~)
side
chain.
relations
transition, the conjugation length, and
there
between
the first optical
are
any
first
angular
correlations
conclude
that
shows
along the backbone,
PPA
one
may
more
the
few
allowing an
angular
correlation
(I,e. a more
ordered
structure)
units
needed
for
over
450 nm
with a band
edge up to
maximum
is roughly
located
optical absorption
whose
at
statistical
length.
fluctuation,
thus a larger
of the
650 nm.
This implies a
decrease
curvature
If
the
On
the
contrary,
configuration
configuration
similar
bears
statistical
on
the
at
the
just
observed
the
the
influence
account
function
statistical
:
conformation
statistical
those
sizc
conformation
scale.
unit
monomer
average
on
conformations
to
poly(2-octyne)
of
spectrum
the
behavior). In fact, we
explicitly into
As for the scattering
taking
influence
absorption
the
localized
observed
for
opposite.
of
effects
of
the
Thus,
in
of
the
saturated
This
as
suggests
a
gr
electrons
much
as
gr
electrons
macromolecule,
polymers (I,e, a
contradiction
apparent
we
more
is
expect
flexible
solved
by
side-groups.
and
steric
the
polymer
interference
chain
of the
in
solution.
side-groups
have
an
N° 3
CONFORMATION
With
ground
a
defined
state
fluctuations
curvature
fluctuations
at
by
measured
are
as
For
temperature.
the
~
where
is
«
For
an
with
the
curvature
:
~~~~
T
macromolecule.
the
substituent
relatively large moment
replaced by equation (17) [8]
thread,
thin
has
macromolecule
isolated
an
infinitely
characterizing the stiffness of the
depending on
side-groups,
of inertia
change the magnitude
can
constant
a
chain
a
k~
0 K,
at
length (20)
statistical
541
POLYACETYLENE
conformation
rod
a
finite
SOLUBLE
OF
extension,
lateral
average
of the
2 E
(I~)
(17)
=
E is
For
the
elastic
circular
a
modulus
kB T
(I~)
and
section,
cross
is
:
b
where
a
Equation (16)
curvature.
is
simply
we
"~
(I~)
effective
average
an
have
of
moment
inertia.
:
~~
~
(18)
=
For
a
ribbon-like
(Fig.10),
structure
principal
the
of
moments
inertia
Ii
are
~
=
~3
~
and
12
~
()~
I~
The
repulsion
steric
=
along the
backbone.
corresponding to the
random
distribution
fluctuations
of
the
influence
The
propagation
of
torsion
ribbon
±
=
4 is the
meant
of
the
4
along
rotation
sign
same
leads
the
to
an
Iii j~ ~/I
4
side
impose
can
torsion
of
implies
groups
substituents
the
of
structure
(l~)
where
substituent
between
backbone.
In
the
effective
average
k~cos~ (p
latter
case,
the
moment
of
inertia
between
monomer
-
units
(Fig, 10)
a2-
~
Sketch
of
the
ribbon
structure
or
with
the
(8)
:
(19)
dp
and
k~
I
=
12
principal
fi
moments
a
torsional
o
al
10.
structure
units
monomer
Ii
Fig.
helical
a
between
torsion
average
an
of
inertia.
(I~/I1)~.
The
two
JOURNAL
542
PHYSIQUE
DE
II
N° 3
planar
ribbon
(4 =0)
rotation
limiting
the
and
gr/2
between
structure
cases
are
a
neighboring
units.
Equations
(18)
and
(19)
quite
well
polydiacetylene
apply
the
to
monomer
polybutylthiophene
[8, 9].
and
cases
10 A corresponding to the
equations (17) and (19) with a~
L~
For PPA
we
use
can
(Fig.
poly(2-octyne),
again
ribbon
like
ll).
For
the
consider
simple
structure
we
a
very
platelets
distributed
only
geometrical form, that is, side groups
described
but
along
as
one
In that case,
conjecture that we can again use our model because the
side of the
backbone.
we
torsion
consider a segment length at a scale
smaller
than
between
the side-groups is large. We
statistical length b
135 A such that the segment
look
the
be
rod,
and
the
at
can
seen
as a
we
=
=
=
angular
correlation
the
~r,,
define
of
the
the
describing
vectors
perpendicular
persistence length
vector
the
to
rod
related
A~
the
to
r~,
torsion
pure
a
Ii
~~
one
can
:
l~(
~~~
~ ~
Using
along the
backbone.
according to equation (5),
torsion
pure
position
the
at
~~~~
~
t
b~)
200
iso
loo
50
0
0
40
20
60
50
4 <degres)
Fig.
Variation
ll.
Ribbon
indicate
For
the
values
segments
n
(«1. «~)
=
of
A (O).
Helical
corresponding
between
(cos (4 ))~
length
statistical
the
10
ai
structure
positions
the
ri
and
in
~
4
is
localization.
length
contour
axis.
;
relation
The
along
torsion
the
For
the
present
implies
this
that
the
between
the
purpose,
we
two
chain
r~,
chain
A~
fp
is the
of the
term
m
and
3.8
A,
the
I-e-
b/2.
=
On
betwee>i
and
F
15
=
monomer
unii~.
A (.),
Arrows
for
random
a
distribution
torsion
of
length responsible of the
w-electron
length b is defined with respect to the axis
consider
another
rotation
4~ related to the helical
be obtain using a
continuous
approximation :
can
contour
have
to
rotations
the
(21)
(cos (~ ) )j
~i
~P
$
length within the period
contour
equation (14), so that we obtain the
axis.
helical
rotation
4~ along the
A~
~
A
poly(2-octyne).
have
chain
A~ «
7.8
=
for
we
torsion
the
0.17, R
:
"
where
of
=
statistical
the
~
root
a
a
~
where
with
obtained
given by
A~ is
and
function
a
torsion
the
to
as
structure
other
hand,
~~~~
P.
ratio
The
relation
For
the
ip/P
between
4
gr
51°
=
rotation
is
the
we
for
given by
rotation
have
4~
the
side
the
square
4 along the
=
58°
groups
and
is
CONFORMATION
N° 3
obtained
groups
for
are
torsion)
length
a
approximated
I-eof
both
on
inertial
and
Such
for
conjecture
a
q
~
inertial
contribution
this
that
means
the
side
the
the
to
groups
inertia Ii and
of
al
a~)
(I
R
~~
the length b the
length b contains
stiffness
local
I~ given by
a)
~~~~
12
'
gr
be
:
approximation used for the theoretical
structure
long
b,
able
calculate
P
to
«
are
as
as
we
an
flexibility given by equations (19) and (23). In other
length scale of the
is
the
structure
compact
at
chain
side
18
may
that
helical
the
Therefore,
within
(the statistical
543
of the
assume
we
to
of
3
reminescent
is
Here
gr/P.
2
b.
«
moments
aj R ~( l
~~
POLYACETYLENE
backbone
the
contribution
equation (19)
with
P/2
=
average
that the
on
such
A,
sides
7.5
P/2
SOLUBLE
OF
factor
average
words,
curvature
fluctuations.
applications,
4 A.
aj
10~° dyne cm~ ~ and a thickness
E
41is a reasonable
preceding
groups
papers [8, 9],
This
point
discussed
value for ai, while the
elastic
modulus
arbitrarily.
is
below.
chosen
was
variations
variations
of b for
different
lateral
lengths are reported in figure11.
These
The
show
both the effect of the size of the side
torsion.
and of the magnitude of the
groups
estimate
We
the
statistical
length using the values given by the fits of the
try to
now
scattering function. Two limiting cases are
describing the chain as a cylinder
considered
:
one
with
second
torsion
deduced
from
the
central
hollow
region, the
using the
a
average
experimental results, but with a random
distribution
torsion
of the sign of the
along the
approximation
backbone.
This
approach has the main
interest
release
the
crude
latter
to
stiffness
describing the inertial
contribution
the
chain
by a homogeneous
dense
to
crossnumerical
For
of
side
the
we
use
elastic
an
modulus
=
discussed
As
in
the
and
R
=
section.
fit,
The
obtained
(Eq. (18))
(I~)
b
to
=
Nevertheless,
accidental,
may
and
this
not
is
expect
cannot
=1.491
aR
to
one
and
of
the
b
146
(19)
leads
for
the
and
4
(23)
and
cylinder
I.
58°,
structure
one
=
obtains
=
accordance
is.
As
between
estimation
computed
above,
noted
parameters
main
accurate
an
equations
with
while
very good
be
used
as
have
7.5i,
=
=
Ii (Fig, ll)
0.55
arbitrarily
with
250i,
the
controlling
of
the
the
effective
and
modulus
local
stiffness
elastic
values,
observed
elastic
constant
E
was
if
not
chosen
(Eq. (17)). One
for a polymer
for a polymer
with
substituents
with
difficult
appears
even
more
repulsions
between
side
As a direct
accurate
consequence,
groups.
an
value of the magnitude of the
units
be
obtained
with
rotation
between
cannot
monomer
our
model.
For
deduced,
26°,
from
statistical
length
example, for PPA the value
the
4
46 I (see Fig. I I),
estimation.
in that
measured, b
be
considered
In addition,
must
as
an
I
the
extension
of
side
of
IQ
value)
is
thus
total
the
about
(the
large,
not
case
groups
a~
very
providing a smooth
variation
of the
statistical
length as function of 4 (Fig, I I ), and therefore a
determination.
Thus, we can only describe in general the behavior
larger uncertainty in the 4
of
macromolecules
with
expecting to obtain in any case the right order
substituents,
without
of magnitude
for the
statistical
length or for the average
in the
of a
ribbon
torsion
case
coil
solution.
in
corresponding
It
steric
=
=
What
structure.
is
remains
that
we
=
polydiacetylene,
are
able
to
describe
essential
features
for
systems
as
polythiophene and polyacetylene.
as
of persistence
It is
interesting to
results
computed
lengths
the
values
to
compare
our
obtained
barrier heights
from
they
by Rossi et al. [10]. Using torsional
obtained
octatetraene,
find A~
60 u and A~
l12 u for the
polyacetylene,
that is a
factor
40 for A~ and 4 for
for
soluble
the
poly(2-octyne)
results.
The
authors
recalled
that
respect
to
A~ with
polyacetylene,
become
irrelevant
if
substituent
alter
the
such a computation
groups
may
potential of the planar
Here
poly(2-octyne)
exhibits
torsion
larger
that
structure.
note
we
a
substituted
diverse
=
JOURNAL
544
thorn
that
calculated
curvature
chains
beyond
It is
structure.
shall
recall
the
few
a
interactions
resonant
observed
increase
scope
them.
It is
neutral
ah
either
lead
not
to
specific
the
3
N°
corresponding
a
of
role
increase
substituents
on
in
the
statistics
of
and
the
effect
disorder
of
the
on
w-electron
exhaustive
list of the various
not to give an
attempts,
first interesting to note that a simple model
considering
excitations
explains rather well the optical absorption
polybutylthiophene in solution [27]. The two other main
initio
approximation,
calculations
disorder
semi-empirical
or
will
reduce
the
models.
In
a
integral (the
transfer
general way,
bandwidth)
gap.
rod
conformation,
and
broadening
the
to
shift
blue
a
of
between
use
the
Compared
induce
does
describe
to
of this
oligothiophenes
the
on
approaches are to
in a tight binding
and
approaches
numerous
are
we
and
again
This
II
solution.
in
There
but
polyacetylene,
emphasizes
for
fluctuation.
PHYSIQUE
DE
a
fluctuations
curvature
of
flexible
in
absorption
visible
the
chains
in
[3].
spectrum
solution
Therefore
red
why color
an
was
reason
transitions
for the
observed
polydiacetylenes (yellow to red (P4BCMU) or yellow to blue
(P3BCMU)),
first explained as a single chain
were
process : a coil to rod change [28].
disorder
induced by
torsional
fluctuations,
devoted
Recently special attention has been
to
excitations
(which may be relevant to a description
either by considering
possible non linear
model, to establish a
of the optical properties of polyaniline [13]) or by using a simple Hiickel
torsional
fluctuation
[10, 11]. If the first,
relationship
between
the optical absorption and the
related
shift (red shift)
corresponds to an
transition
is directly
the gap,
lowest
to
any blue
(decrease) of the band gap. Modelling that behaviour
the basic aim of Rossi et al.
increase
was
~~
(cos~11 ~~~) (where p~ and p~ are the
[10]. Using a band gap given by : E~
2[ p~[ (1
fld
shifts
have
been
attributed
increase
to
stiffness.
chain
in
This
the
=
integral
transfer
calculated
The
ridigity
of
the
at
large
with
the
chain
Indeed,
backbone.
This
pertinent
of
color
that
means
when
parameter
torsion
sites
for
gr
scale.
The
solution
existence
the
correspond
to
an
along
the
which
exactly
absorption
flexible
One
in
shows
substituent
the
side
backbone
a
this
maximum
groups,
conformations
plays only
fluctuation
curvature
torsion
with
of
need
not
units
work
they
bonds),
double
rotation
acts
chemical
a
as
considered.
do
we
and
where
also
monomer
present
single
the
limit
delocalization.
electrons
between
transparent
a
because
exhibiting
solutions
the
to
unit
monomer
giving
stiffer
range.
neighbor
nearest
macromolecule
conformation
confined
the
average
the
breaking
principal
defect
between
(cos 2 ii. The strong disorder
conjugation length [29, 30], was
merit
of the
latter
approach is that
the
of
consider
cart
of
kind
located
minor
role
or
a
behavior,
the
in
are
the
U-V-
expect
may
with the
one
least
at
the
rod
w-electrons
the
polymers
between
occurs
directly
relate
to
is
not
that
same
the
units.
monomer
direct
comparison of the
statistical
conformation
of PPA
with
the
polystyrene chains does not show a sizeable
enhancement
of the chain
stiffness.
It has been predicted that the gain in energy
due to
electron
delocalization
either in
the
doped or neutral
be
it
large
that
could
the
contribution
of
state
can
so
overcome
conformational
might
consider
that
the
contribution
of
the
entropy [4, 5]. Typically,
one
transfer
integral p is about I eV, I-e- much
than kT.
With a model
based
exclusively on
more
w-electron
interactions
fails to take
between
units
that
into
sterically
the
induced
account
torsion, Spiegel et al. [5] calculate a statisticaL length of about 150
units, an order of
monomer
magnitude larger than the one
measured.
Actually, R-R-Sstudies
found
similar
spectra in
On
the
other
homologous
film
and
in
hand,
saturated
solution,
suggesting
that
consider
that
steric
interference
may
backbone
regardless of its effect on
conformation
in
solution.
Therefore,
the
electronic
between
the
chain
it is
quite
structures
substituents
packing
in
difficult
to
are
very close in
controls
the local
the
solid
estimate
state
the
or
exact
both
order
on
One
states.
along
the
influence
the
statistical
of the
CONFORMATION
N° 3
conjugated
soluble
result
Indeed,
delocalization.
electron
for
shows
best
at
it
SOLUBLE
POLYACETYLENE
questionable
as
OF
becomes
the
polymers
within
effect, if any.
weak
a
current
state
to
wether
of
the
545
it
be
can
measured
Still,
science.
all
at
present
our
Conclusion.
5.
In
work
this
study
have
we
conformation
and
responsible
model
the
localization
of
gr
helical
the
to
A
on
along
torsion
random
natural
chain
spring-like
Various
structure
of
15
A,
20
present
enabled
but
The
methyl
does
group
in a
result
not
to
us
localization.
of the
existence
torsion,
average
and
induces
that
chain
on
the
controlling
driving parameter
poly(2-octyne), the
the
polymers,
The
torsion
parameter
also
between
torsion
the
is
the
conjugation.
for
main
is the
it
of
one
average
backbone
of
larger
expanding
in
now
would
examine
be to
controlling
better
a
efforts
are
the
work
aim
the
with
structure
backbone.
octyne)
of this
with
torsion
second,
effect
polyacetylenes,
chain.
the
continuation
structure
of
For
the
on
substituted
two
pitch length lying
a
clearly responsible
is
information
average
and
electrons.
magnitude
destroys the
backbone
the
polymer
with
structure
assign the
order
of
corresponding torsion
close
first,
of
an
:
that,
conformation
for
used
quantitative
configuration. With
obtain
to
unambiguously
shows
statistical
the
tried
electrons
gr
the
[31],
for
region and
insights gained from
hollow
central
on
it
effects
of
example
the
obtain
smaller
a
study
substituents
various
to
torsion
of
PPA
helical-
an
along the
and poly(2-
progress.
Acknowledgments.
We
for
would
the
like
thank
to
time
beam
Timmins
Peter
allocation
and
for
Mireille
his
Institut
Laue-Lartgevin
help during experiment,
for performing the light scattering study on
Adam
poly(2-octyne).
References
[Ii EXARHOS G. J., RISEN W. M., BAUGHMAN R. H., J. Am. Chem. Sac.
[2] SHAND M. L., CHANCE R. R., LE POSTOLLEC M., SCHOTT M., Fhys.
[3] Soos Z. G., SCHWEIzER K. S., Chem. Fhys. Lett. 139 (1987) 196.
[4] PINCUS P. A., ROSSI G., CATES M. E., Europhys. Lett. 4 (1987) 41.
[5] SPIEGEL D. R., PINCUS P. A., HEEGER A. J., Synth. Met. (Switzerland)
16]
[7]
(1976)
B 25
28
481.
(1982)
(1989)
4431.
C385.
G., MULLER M. A., SCHMIDT M., WEGNER G.,
Macromolecules
837.
17 (1979)
RAWISO M.,
AIMt J. P., FAVE J. L., SCHOTT M.,
MULLER M. A., SCHMIDT M.,
BAUMGARTL
WEGNER G., J. Fhys.
France
861.
49 (1988)
WENz
[8] AIML J. P.,
BARGAIN
characterization
Conjugated
Dordrecht,
[9]
98
Rev.
F.,
Europhys.
conjugated
Polymers,
J.L.
of
1991) pp.
Lett.
9
(1989)
polymer
Bredas
and
35.
For
solutions
in
R.Silbey
a
the
Eds.
review
J.
AIMt
AIMt
and
J. P.,
Structural
doped
state
in
Publishers,
Academic
229-314.
RAMAKRISHNAN
P.,
S., CHANCE R. R., KIM M. W., J. Fhys.
J. P., GARRIN P., BAKER G. L.,
RAMAKRISHNAN S., TIMMINS P.,
AIMt
see
undoped
(Kluwer
H.,
Fiance
Synthetic
51(1990)
Met.
41
963 ;
(1991)
859.
[10]
[I II
[12]
[13]
[14]
CHANCE R. R., SILBEY R., J.
Chem. Fhys. 90 (1989) 7594.
A., ROSSI G., J. Chem. Fhys. 92 (1990) 4548.
BREDAS J. L.,
HEEGER A. J.,
Macromolecules
l150.
23 (1990)
GINDER J. M., EPSTEIN A. J., Fhys. Rev. B 41 (1990)
10674.
AIMt J. P., BARGAIN F., SCHOTT M.,
MULLER M. A., ECKHARDT H.,
ELSENBAUMER
ROSSI
G.,
VIALLAT
Rev.
[15]
MASUDA
(1989)
Lett.
62
T.,
HIGASHIMURA
55.
T.,
Adv.
Folym.
Sci.
81(1986)
121.
R.
L., Fhys.
546
JOURNAL
PHYSIQUE
DE
II
3
N°
[161 ABE Y., MASUDA T., HIGASHIMURA T., J. Folym. Sci. Folym. Chem. Ed. 27 (1989) 4267.
[171 BATCHELDER D. N., BLOOR D., Advances in Infrared and Raman Spectroscopy 11, R. J. H. Clark
and
[181
R. E.
OBERTHOR
Eds.,
Hester
C.,
R.
M.,
I-L-L-
D.,
133-209.
pp.
intemal
report
H.,
OBERTHUR R. C.,
Makromol.
Chem.
186 (1985)
1701.
G., Les polymbres en solution,
mod£lisation
leur
leur
structure
et
(Editions de Physique, les Ulis, France, 1987).
[201 LANDAU L. D., LIFSHITz E. M., Stat. Fhys. 2nd Ed. (Pergamon Press, London, 1959) p. 478.
[211 YOSHIzAKI T., YAMAKAWA H.,
Macromolecules13
(1980) 1518.
[221 DES CLOIzEAUX J.,
Macromolecules
6 (1973) 403.
RAGNETTI
[191 DES
[23]
[241
GEISER
J.,
CLOIzEAUX
Angle X-ray
Small
KOYAMA
H.,
(1991)
Roth
JANNINK
ScaItering,
YOSHIzAKI
T.,
O.
Glatter
EINAGA
and
Y.,
O.
Kratky
HAYASHI
Eds.
H.,
(Acad.
YAMAKAWA
Press.,
H.,
New
1982).
York,
Macromolecules
24
932.
[251 SEARS V. F.,
[261 PRINGLE O.,
[271 FAVE J. L.,
S.
HOCKER
AECL-8490,
SCHMIDT
to
Eds.
be
P.
Chalk
W.,
J.
River
Nuclear
Appl. Cryst.
4
Laboratories,
Ontario,
Canada
(1984).
(1971) 290.
published in
Electronics
properties of polymers,
(Springer, 1991).
K. C., HEEGER A. J., Fhys. Rev.
51(1983)
Lett.
[281 SINCLAIR M., LIM
[291 SCHWEIzER K. S., J. Chem. Fhys. 85 (1986) l156.
[301 SURJAN P. R., KUzMANY H., Fhys. Rev. B 33 (1986) 2615.
[311 CLOUGH S. B., SUN X. F., TRWATHY S. K., BAKER G. L.,
H.
Kuzmany,
1768
Macromolecules
and
M.
references
24
(1991)
Meriting,
therein.
4264.